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Consider the multiplication problem 1089 × 9 = 9801. The product 9801 is a flipped-around version of the number 1089!
Let us say that the number 1089 is flipped when multiplied by 9. Which four-digit numbers (if any) are flipped when multiplied by 4? |
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Follow-up ChallengesIs 1089 the only four-digit number that is flipped when multiplied by 9?
Are there any three-digit or five-digit numbers that are flipped when multiplied by 9? What about when multiplied by 4? Are there any numbers that are flipped when multiplied by 3? What about when multiplied by 5? Several of the response videos use clever reasoning to narrow their search. Explain why the solution to the challenge has to be between 2000 and 2499. In her response video, Ashlyn goes further and narrows the search to numbers between 2000 and 2250. Explain her reasoning in your own words. |
Response Videos
Ashlyn's video response
Erika's response video
Erin's response video
Thoughts on the challenge, plus a new observation about the number 1089, from Wynne
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